[libcxx-commits] [PATCH] D128146: [libc++] Use uninitialized algorithms for vector

[Nico Weber via Phabricator via libcxx-commits]

thakis added a comment.

Hello, this changes behavior for the following program. Is that intentional? (It has an easy workaround -- just remove that defaulted ctor, and we only hit it in a single place as far as I know, so it's not a big problem for us -- but I thought I'd check if the change in behavior is intentional)

  $ cat test.cc
  #include <vector>
  
  class Instruction {
   public:
    int i;
  };
  class StructuredControlState {
   public:
    StructuredControlState(Instruction* break_merge, Instruction* merge)
        : break_merge_(break_merge), current_merge_(merge) {}
    StructuredControlState(const StructuredControlState&) = default;
    bool InBreakable() const { return break_merge_; }
    bool InStructuredFlow() const { return CurrentMergeId() != 0; }
    uint32_t CurrentMergeId() const;
    uint32_t CurrentMergeHeader() const;
    uint32_t BreakMergeId() const;
    Instruction* BreakMergeInst() const { return break_merge_; }
   private:
    Instruction* break_merge_;
    Instruction* current_merge_;
  };
  class MergeReturnPass {
    void GenerateState() {
      Instruction inst;
      v.emplace_back(&inst, &inst);
    }
    std::vector<StructuredControlState> v;
  };

Before this change:

  $ third_party/llvm-build/Release+Asserts/bin/clang -I buildtools/third_party/libc++/trunk/include/ -c test.cc -I buildtools/third_party/libc++ -nostdinc++ -std=c++17 -Wall  -Wdeprecated-copy
  # fine

After this change:

  $ third_party/llvm-build/Release+Asserts/bin/clang -I buildtools/third_party/libc++/trunk/include/ -c test.cc -I buildtools/third_party/libc++ -nostdinc++ -std=c++17 -Wall  -Wdeprecated-copy
  test.cc:11:3: warning: definition of implicit copy assignment operator for 'StructuredControlState' is deprecated because it has a user-declared copy constructor [-Wdeprecated-copy]
    StructuredControlState(const StructuredControlState&) = default;
    ^
  buildtools/third_party/libc++/trunk/include/__algorithm/move.h:33:15: note: in implicit copy assignment operator for 'StructuredControlState' first required here
      *__result = std::move(*__first);
                ^
  buildtools/third_party/libc++/trunk/include/__algorithm/move.h:52:17: note: in instantiation of function template specialization 'std::__move_impl<StructuredControlState *, StructuredControlState *, StructuredControlState *>' requested here
      return std::__move_impl<_InType*, _InType*, _OutType*>(__first, __last, __result);
                  ^
  buildtools/third_party/libc++/trunk/include/__algorithm/move.h:84:8: note: in instantiation of function template specialization 'std::__move_impl<StructuredControlState, StructuredControlState, void>' requested here
    std::__move_impl(__last_base, __first_base, __result_first);
         ^
  buildtools/third_party/libc++/trunk/include/__algorithm/move.h:94:21: note: in instantiation of function template specialization 'std::__move_impl<StructuredControlState *, StructuredControlState *, 0>' requested here
    auto __ret = std::__move_impl(std::__unwrap_iter(__first), std::__unwrap_iter(__last), std::__unwrap_iter(__result));
                      ^
  buildtools/third_party/libc++/trunk/include/__algorithm/move.h:110:15: note: in instantiation of function template specialization 'std::__move<std::reverse_iterator<StructuredControlState *>, std::reverse_iterator<StructuredControlState *>, std::reverse_iterator<StructuredControlState *>>' requested here
    return std::__move(__first, __last, __result).second;
                ^
  buildtools/third_party/libc++/trunk/include/__memory/uninitialized_algorithms.h:635:17: note: in instantiation of function template specialization 'std::move<std::reverse_iterator<StructuredControlState *>, std::reverse_iterator<StructuredControlState *>>' requested here
      return std::move(__first1, __last1, __first2);
                  ^
  buildtools/third_party/libc++/trunk/include/vector:914:27: note: in instantiation of function template specialization 'std::__uninitialized_allocator_move_if_noexcept<std::allocator<StructuredControlState>, std::reverse_iterator<StructuredControlState *>, std::reverse_iterator<StructuredControlState *>, StructuredControlState, void>' requested here
      __v.__begin_   = std::__uninitialized_allocator_move_if_noexcept(
                            ^
  buildtools/third_party/libc++/trunk/include/vector:1581:5: note: in instantiation of member function 'std::vector<StructuredControlState>::__swap_out_circular_buffer' requested here
      __swap_out_circular_buffer(__v);
      ^
  buildtools/third_party/libc++/trunk/include/vector:1600:9: note: in instantiation of function template specialization 'std::vector<StructuredControlState>::__emplace_back_slow_path<Instruction *, Instruction *>' requested here
          __emplace_back_slow_path(_VSTD::forward<_Args>(__args)...);
          ^
  test.cc:25:7: note: in instantiation of function template specialization 'std::vector<StructuredControlState>::emplace_back<Instruction *, Instruction *>' requested here
      v.emplace_back(&inst, &inst);
        ^


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D128146/new/

https://reviews.llvm.org/D128146